client: Only connect to Collab automatically for Zed staff (#35827)

This PR makes it so that only Zed staff connect to Collab automatically.

Anyone else can connect to Collab manually when they want to collaborate
(but this is not required for using Zed's LLM features).

Release Notes:

- N/A

---------

Co-authored-by: Richard <richard@zed.dev>

crates/feature_flags/src/feature_flags.rs

@@ -158,6 +158,11 @@ where
     }
 }
 
+#[derive(Debug)]
+pub struct OnFlagsReady {
+    pub is_staff: bool,
+}
+
 pub trait FeatureFlagAppExt {
     fn wait_for_flag<T: FeatureFlag>(&mut self) -> WaitForFlag;
 
@@ -169,6 +174,10 @@ pub trait FeatureFlagAppExt {
     fn has_flag<T: FeatureFlag>(&self) -> bool;
     fn is_staff(&self) -> bool;
 
+    fn on_flags_ready<F>(&mut self, callback: F) -> Subscription
+    where
+        F: FnMut(OnFlagsReady, &mut App) + 'static;
+
     fn observe_flag<T: FeatureFlag, F>(&mut self, callback: F) -> Subscription
     where
         F: FnMut(bool, &mut App) + 'static;
@@ -198,6 +207,21 @@ impl FeatureFlagAppExt for App {
             .unwrap_or(false)
     }
 
+    fn on_flags_ready<F>(&mut self, mut callback: F) -> Subscription
+    where
+        F: FnMut(OnFlagsReady, &mut App) + 'static,
+    {
+        self.observe_global::<FeatureFlags>(move |cx| {
+            let feature_flags = cx.global::<FeatureFlags>();
+            callback(
+                OnFlagsReady {
+                    is_staff: feature_flags.staff,
+                },
+                cx,
+            );
+        })
+    }
+
     fn observe_flag<T: FeatureFlag, F>(&mut self, mut callback: F) -> Subscription
     where
         F: FnMut(bool, &mut App) + 'static,